The broad objective of the proposed research is to determine whether influenza virus hybrids (recombinants) that might occur in nature, as a result of a mixed infection in an animal species, can be maintained in that or another species. It has been shown under experimental conditions that recombinant influenza viruses can be recovered from turkeys and pigs after exposure to antigenically distinct influenza A viruses. There is reason to suspect that new pandemic strains of influenza viruses may arise in this manner. The research will be directed toward the study of selected aspects of the pathogenesis of recombinant influenza virus infection in swine and turkeys which will include the following: 1) Determine the relative infectivity and pathogenicity of 6 recombinant viruses in the 2 host systems; 2) Determine intraspecies and interspecies transmissibility of 2 selected recombinants under simulated natural conditions; and 3) Determine the effect of "forced" transmission on the host and the virus. In Phase I (No. 1 above) the 2 hosts will be infected with 6 recombinant viruses. Three of the recombinants will have the swine influenza hemagglutinin with 3 different neuraminidases. The other 3 recombinants will have an avian hemagglutinin (Hav6) with the same 3 neuraminidases as above. The infectivity and pathogenicity will be evaluated on the basis of the host response, duration of virus shedding, and lesions as compared to infections with the "parent" swine influenza and avian influenza viruses. In Phase II, 2 recombinants, selected on the basis of the results obtained in Phase I, will be used for transmission studies. Animals will be infected and placed with susceptible animals and additional susceptibles will be added to the herd periodically to determine whether the virus can be maintained in a population. Both intraspecies and interspecies transmission will be studied. Two viruses that have relatively poor infectivity will be "force passed" to evaluate the ease or difficulty of host adaptability.